In liquid crystal displays, touch panels, organic electroluminescences and the like, there have been used various kinds of protective films or insulating films. For example, an epoxy resin film formed by a wet process is used as a protective film for protecting a liquid-crystal display color filter in usual.
On the other hand, the insulating films are exemplified by those for use in TFT (thin-film-transistor), i.e., by those used for TFT liquid-crystal displays. There has been used a SiN film formed mainly by CVD process (Chemical Vapor Deposition) therefor.
The protective films and insulating films are required to be made from material that allows forming a film by wet process, the material having a further enhanced heat resistance in order to correspond to recent TFT liquid-crystal displays getting increased in response speed and in brightness of the back light source, the material being easier in film formation and superior in cost to conventional materials.
As an example of the material, it is possible to cite a silane condensate obtained by the hydrolysis and condensation reaction of alkoxysilanes (hereinafter, sometimes referred to as merely a condensate). Such a condensate is excellent in heat resistance, transparency in the visible range, and an adhesion to a glass or silicon substrate. Moreover, by specifying the kind and the composition of alkoxysilanes used as raw materials and by devising a production method, the condensate comes to exhibit high solubility in organic solvents. The above-mentioned condensate can form a film through wet process to serve as a protective or insulating film for a semiconductor device or a display.
The silane condensate also becomes usable as a hardmask, by increasing the silicon content in the condensate. More specifically, an organic polymer to be used as an insulating film for an integrated circuit is an organic substance as well as a resist film, so that it is difficult to attain a high etching rate at the time of dry etching if the resist film is superimposed on the insulating film. For this reason, a layer referred to as a hardmask and different from the insulating film and resist film in reactivity has been effectively disposed between the insulating film and resist film, in which silicon oxides and silicon nitrides have generally been used as the hardmask.
In the field of display and semiconductor, a substrate is often processed to have variously shaped thin films thereon, in which case photolithography is employed. Photolithography is a technique of exposing a resist film formed on a substrate such as a glass substrate and a silicon substrate to irradiation through a photomask and then transcribing a pattern of the photomask to the resist film by utilizing the difference of solubility between an irradiated portion and non-irradiated portion thereby forming a resist pattern. In the case of forming a pattern on a protective film or an insulating film, photolithography is conducted to form a resist pattern on the films, followed by performing dry etching to form a pattern.
In view of the above, there have been developed some resist materials that use silane condensate, the resist materials allowing a pattern formation by photography without a hardmask and not requiring forming a protective film or insulating film and a resist film independently (see Patent Documents 1-4). When these resist materials are used, it becomes possible to obtain a resist film achieving a performance as the protective film or insulating film and therefore it becomes possible to shorten the manufacturing time and to reduce the manufacturing cost.
In Patent Document 1, there is disclosed a negative resist material characterized by incorporating a resin having silanol groups and a compound which generates an acid by irradiation with high-energy beams.
In Patent Document 2, there is disclosed a photosensitive resin composition that contains, as its primary components, (1) an alkali-soluble siloxane polymer having methyl groups each directly combined with a silicon atom and silanol groups, wherein the content of silanol is 0.1-2.0 (the content of silanol is indicated by the absorbance ratio of the silanol group (900 cm−1) to the silicon-methyl group (1271 cm−1) at each absorption peak by the infrared spectroscopic analysis, and more specifically, indicated by “Abs(900 cm−1)/Abs(1271 cm−1)”, (2) a compound to generate a reaction accelerator by action of radiation, and (3) a solvent.
In Patent Document 3, there is disclosed: a composition for forming a film, which comprises (A) an alkoxysilane condensation product produced by reacting a component (X) comprising phenyl triethoxysilane or phenyl trimethoxysilane, a component (Y) comprising methyl triethoxysilane or methyl trimethoxysilane and a component (Z) comprising triethoxysilane or trimethoxysilane at a certain ratio any ratio and (B) an acid generator which can generate an acid upon being exposed to an external stimulation such as light or heat; a method for producing a patterned film by using the composition; and an insulation film for an electronic device.
In Patent Document 4, there is disclosed a radiation curable composition that contains: a siloxane resin including a resin obtained by hydrolyzing and condensing essential components including a specified siloxane compound, a polymer or a partial condensate of the siloxane compound; a photo-acid generating agent or an optical base generating agent; and a solvent capable of dissolving the siloxane component and containing an aprotic solvent, where the siloxane compound includes tetraalkoxy silane and trialkoxy silane. Incidentally, the photo-acid generating agent is to generate acid by being irradiated with high-energy rays such as ultraviolet rays, X-rays and electron beams.
From the viewpoint of using a silane condensate obtained by hydrolysis and condensation reaction of alkoxysilanes as material for protective film, material for insulating film or material for resist film, there exist three problems as follows, for example.
The first problem resides in the storage stability of the condensate in itself. In the use of alkoxysilanes as the raw material, silanol (Si—OH) groups that remain in the condensate causes condensation reaction little by little during storage so as to increase in molecular weight and then becomes insoluble in an organic solvent at the time of being used as an application liquid, with which the application liquid is so increased in viscosity as to be difficult to form a film with uniform thickness.
The second problem is that a hard film with no cracks is difficult to obtain. Even in a case of attempting to form a hard silica film on a substrate by adjusting alkoxysilanes to be used in the condensate in terms of kind and composition ratio, the film is apt to be damaged by generation of cracks during baking particularly when it has a heavy thickness. For example, a protective film or insulating film for use in a semiconductor integrated circuit, having a thickness of at least 3.0 μm, is required to have a pencil hardness of at least 5H. It is difficult, for a silica film obtained by baking a silane condensate, to produce a film having a thickness of at least 3.0 μm, a pencil hardness of at least 5H and no cracks. If a silane compound e.g. a siloxane compound is used as a composition for a resist film, it acts as an insulating film or protective film for a semiconductor integrated circuit and remains on the circuit in contrast to an organic resist film, and therefore desired to be a hard film having no cracks.
The third problem is that cissing and unevenness are apt to occur in of the film when the condensate is applied to a substrate such as silicon substrate and a glass substrate as an application liquid.